Lead-acid batteries have a casing with a plurality of internal, paste filled, grid plates and separators that are submerged in acid. The grid plates and separators are tightly compacted elements. During the manufacture of the batteries it is necessary to fill the case with the acid after the grid plates are installed. It is imperative to completely fill the case and also to fully saturate the separators. This can be a time consuming operation which increases the cost of production as the fill time increases, particularly when the separators are made with absorbent glass mat material.
Many methods have been considered or undertaken in an effort to reduce the fill time. It has been proposed to roll the battery case to lie on one side and then partially submerge the case in an acid bath. This method results in an unknown quantity of acid fill and is too time consuming. Another method that has been considered also lays the battery case on the side and attaches a manifold to ports on the "top" so that acid can be metered into the case through the manifold. This method is also very time consuming and total saturation of the separators is virtually impossible.
Yet another method that has been considered includes applying a vacuum to the case to evacuate the air and introduce acid into the interior of the case. This method results in dry spot in the separators and acid damage to the vacuum equipment. Still another method used a pulse vacuum to evacuate the air while acid is introduced through the bottom of the case. The case could not be reliably sealed following the fill operation. A further method included pouring acid directly into the top of the battery case. This method results in trapped air, which creates dry spots in the separators, insufficient acid fill and excessive fill time.